Edit the Ceph CRUSHmap

The CRUSHmap, as suggested by the name, is a map of your storage cluster. This map is necessary for the CRUSH algorithm to determine data placements. But Ceph’s CRUSHmap is stored in binary form. So how to easily change it?

Native tools

Ceph comes with a couple of native commands to do basic customizations to the CRUSHmap:

Read and write the map

If you want to customize anything else (not covered in ceph osd crush) then you will need to download the CRUSHmap, edit it and then upload the new version. But since the CRUSHmap is in binary format you have to convert it to and from human readable text.